With the rapid development of video monitoring technology, requirement of the users for monitoring system is getting higher and higher. A very significant point is that they expect the monitoring system can provide more intelligent functions. Video motion analysis function is a very basic and important function among the various intelligent functions. The so-called video motion analysis means detecting screen changes of specific area and moving objects in video screens of specific video scenes and eliminating interference from normal light change and noise, and then providing useful information for subsequent alarm, target classification and target tracking.
In the video code stream motion analysis of the prior technology, such as a Chinese Patent No. CN03103526.4 discloses an analysis method based on the average size of inter-frame coding picture. The motion information is detected by calculating average size of video frames which is inter-frame coded and change rate of the average size in the above patent. The inventors of the present invention have found that: first of all, as influenced by code-rate control module in code stream encoding, even static code streams of two neighboring frames may have larger difference in size because the difference of the used quantized coefficients may be greater, whereas all video frames are coded only using one same quantized coefficient and only video that contain a large amount of motion information can be effectively detected in this method. For the above, the method in above patent can cause faulty motion determination. Secondly, if there are slowly moving objects exist in the video and the sizes of these objects account for a smaller proportion of the total picture, the moving objects are unable to effectively detect by the method as size of the code stream does not change significantly, when the sequence is encoded using the same quantized coefficient. Last, the determination of this method is based on size of code stream of the whole picture, which is unable to detect areas happened movement and direction of moving object, though it can detect if there exists a moving object in video. In a word, the method can only accomplish simple motion detection, but is unable to adapt various coded code stream and scenarios.
The inventors of the present invention also found that coding end can provide limited information and process limited computation in the video motion analysis method using coding ends information in prior art. Therefore, the accuracy is not high and this kind of methods have rigorous requirement for video scenes and most of them can only be applied for simple indoor scenes instead of complicated outdoor scenes. Similarly, the video motion analysis method based on decoding pictures figures out decoding pictures by decoding compressed code stream and then counts pixel features of the decoding pictures and performs motion analysis according to these features, therefore the defect of this kind of methods is that a great deal of computation and larger storage space are needed for computing coding pictures and performing motion analysis on decoding pictures, which result in a difficult in achieving real-time processing result. On the other hand, its operation accuracy is low because most of decoding pictures are distorted.
The inventors of the present invention also found that there exist following methods to implement video code stream conversion method and overcome its defect in prior conversion technology:
Firstly, dual code stream method. One code stream with lower resolution or frame rate is coded in this kind of method besides coding one code stream with normal resolution and frame rate. The two code streams are used for storage and network forwarding, respectively. Load of coding end and transmission load from coding end to receiving end increased as two code streams need to be coded while code stream with lower resolution and frame rate may lead to key information missing.
Secondly, transcoding storage method. This kind of methods transform received code stream to code stream with lower resolution or frame rate by a specific algorithm, so as to reduce required storage space when storing a code stream. Transcoding process is added to receiving apparatus in the method which have to consume greater calculated quantity. Moreover, transcoded code stream will inevitably cause missing of information of the picture as its low frame rate and resolution.
Thirdly, code stream extraction method. This kind of methods extract coding code stream corresponding to some frames or field for reference out of video code stream and discard coding code stream corresponding to other frames or field not for reference. The method has less calculated quantity than above two methods. However, it still has a problem of information missing as discarded frames may contain key motion information.
Otherwise, as IP cameras provide more information by providing pictures with increasing high resolution and frame rate in monitoring field, transmission and processing of the video code stream lead to severe pressure on network bandwidth and storage.
Therefore, how to achieve more effectively, stronger and wider range video motion analysis and how to reduce pressures of network bandwidth and storage caused by video code stream are urgent problems for people to solve.